The numbers for jatropha are on p284. Even if all of Africa were completely
covered with jatropha plantations, the power produced, shared between
six billion people, would be 8 kWh/d per person (which is only one third
of today’s global oil consumption). You can’t fix your oil addiction by
switching to jatropha!

Let’s estimate a bound on the power that energy crops could deliver for
the whole world, using the same method we applied to Britain in Chapter
6: imagine taking all arable land and devoting it to energy crops. 18% of
the world’s land is currently arable or crop land – an area of 27 million
km2. That’s 4500 m2 per person, if shared between 6 billion. Assuming a
power density of 0.5 W/m2, and losses of 33% in processing and farming,
we find that energy crops, fully taking over all agricultural land, would
deliver 36 kWh/d per person. Now, maybe this is an underestimate since
in figure 6.11 (p43) we saw that Brazilian sugarcane can deliver a power
density of 1.6 W/m2, three times bigger than I just assumed. OK, maybe
energy crops from Brazil have some sort of future. But I’d like to move on
to the last option.

Solar heaters, solar photovoltaics, and concentrating solar power

Solar thermal water heaters are a no-brainer. They will work almost every-
where in the world. China are world leaders in this technology. There’s
over 100 GW of solar water heating capacity worldwide, and more than
half of it is in China.

Solar photovoltaics were technically feasible for Europe, but I judged
them too expensive. I hope I’m wrong, obviously. It will be wonderful
if the cost of photovoltaic power drops in the same way that the cost of
computer power has dropped over the last forty years.

My guess is that in many regions, the best solar technology for electric-
ity production will be the concentrating solar power that we discussed on
pages 178 and 236. On those pages we already established that one billion
people in Europe and North Africa could be sustained by country-sized
solar power facilities in deserts near the Mediterranean; and that half a
billion in North America could be sustained by Arizona-sized facilities in
the deserts of the USA and Mexico. I’ll leave it as an exercise for the reader
to identify appropriate deserts to help out the other 4.5 billion people in
the world.

The bottom line

The non-solar numbers add up as follows. Wind: 24 kWh/d/p; hydro:
3.6 kWh/d/p; tide: 0.3 kWh/d/p; wave: 0.5 kWh/d/p; geothermal:
8 kWh/d/p – a total of 36 kWh/d/p. Our target was a post-European
consumption of 80 kWh/d per person. We have a clear conclusion: the
non-solar renewables may be “huge,” but they are not huge enough. To